Polarization mode switching semiconductor laser apparatus

ABSTRACT

A semiconductor laser apparatus includes a semiconductor substrate, a first cladding layer, an active layer, a second cladding layer, a second electrode, and a pair of resonator mirrors. The semiconductor substrate has a first electrode on one surface. The first cladding layer is formed on the other surface of the semiconductor substrate. The active layer is placed on the cladding layer. The second cladding layer is placed on the active layer. The second electrode is placed on the second cladding layer. The pair of resonator mirrors are placed in a waveguide direction perpendicular to the surfaces of the semiconductor substrate to oppose each other. The active layer is constituted by a quantum well layer having a tensilely strain. The second electrode is separated into portions not less than two portions.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor laser apparatus.

Since semiconductor laser apparatuses currently used are compact andefficient, a rapid improvement in optical sensing techniques such as anoptical recording technique has been achieved. However, in considerationof a sensing technique using polarized light, a light source capable ofpolarization control is indispensable.

Conventional polarization control in semiconductor laser apparatusesrequires an optical system for controlling a reflection loss by using 35polarizers and the like. For this reason, the size of each element isincreased, or an unstable operation results from a positional shift incomponents.

Consider oscillation mode control in the semiconductor laserapparatuses. Generally, oscillation is produced in only the TE mode (inwhich electric field components are parallel to the active layer), or inonly the TM mode (in which magnetic field components are parallel to theactive layer) by applying a tensilely strain to the active layer toincrease the gain of the TM mode.

FIGS. 29A and 29B show a conventional semiconductor laser apparatus.Referring to FIGS. 29A and 29B, reference numeral 1 denotes asemiconductor substrate; 2, an active layer consisting of GaAs; 3, anupper cladding layer consisting of AlGaAs; 4, a lower cladding layerconsisting of AlGaAs; 5, an insulating layer consisting of SiO₂ ; 6, anupper electrode; 7, a lower electrode; 8 and 9, resonator mirrors; and10, a optical waveguide stripe.

In this semiconductor laser apparatus, since the active layer is a bulkmember, there is no difference between the gain obtained by currentinjection in the TE mode (in which an electric field is parallel to theactive layer) and that in the TM mode (in which an electric field isperpendicular to the active layer). However, the reflectance of eachresonator mirror is higher in the TE mode than in the TM mode. For thisreason, the semiconductor laser mainly oscillates in the TE mode. Inthis case, the light intensity of the TM mode is not more than 1/100that of the TE mode.

If a quantum well structure having no strain or having a compressivelystrain is used for the active layer, since electrons in a conductionband are mainly combined with heavy holes in a valence band, the gainobtained by current injection in the TE mode is higher than that in theTM mode. Owing to this high gain in the TE mode as well as the effect ofthe reflectance of each resonator mirror, the laser apparatus is causedto oscillate in the TE mode.

In contrast to this, if a quantum well layer having a stretching strainis used for the active layer, since electrons in a conductive band aremainly combined with light holes in a valence band, the gain obtained bycurrent injection in the TM mode is higher than that in the TE mode. Ifthis effect is greater than the effect of the reflectance of eachresonator mirror, the laser apparatus is caused to oscillate in the TMmode.

As described above, the conventional semiconductor laser apparatusesoscillate either in the TE mode or in the TM mode.

In digital optical communications in which polarized light beams areassigned to information "0" and information "1", polarizationinterference optical systems for heterodyne detection, optical sensorsbased on differences in reaction to polarized light, and the like, boththe TE and TM modes are required. In such a case, if a conventionalsemiconductor laser apparatus is used, a wave plate for convertingpolarized light of the TE mode into that of the TM mode is required.Generally, a wave plate is made of an expensive dielectric crystalhaving birefringence, and is inserted, as a discrete component, in anoptical system. Therefore, the following problems are posed, forexample:

(1) In order to convert the polarization state of one light beam, amechanism for rotating or moving the wave plate is required. Inaddition, the conversion speed is low.

(2) With a reduction in the size of the optical system, a cumbersomepositioning operation is required for assembly, resulting in an increasein the cost of the optical system.

SUMMARY OF THE INVENTION

It is, therefore, a principal object of the present invention to providea semiconductor laser apparatus which can easily select polarization inthe TE or TM mode.

It is another object of the present invention to provide a semiconductorlaser apparatus which can easily select polarization in the TE or TMmode without using special components.

It is still another object of the present invention to apply thesemiconductor laser apparatus of the present invention to an informationrecording/reproducing apparatus, an optical sensor, an optical encoder,or a display apparatus so as to provide an apparatus smaller in sizethan a conventional apparatus.

In order to achieve the above objects, the gain of the TM mode isincreased by using a quantum well structure having a tensilely strainfor the active layer, and the loss difference and gain differencebetween the TE and TM modes are switched in magnitude by dividing acurrent injection region between resonator mirrors, thereby allowingselection of polarization in the TE or TM mode.

According to an aspect of the present invention, there is provided asemiconductor laser apparatus comprising a semiconductor substratehaving a first electrode on one surface, a first cladding layer formedon the other surface of the semiconductor substrate, an active layerplaced on the cladding layer, a second cladding layer placed on theactive layer, a second electrode placed on the second cladding layer,and a pair of resonator mirrors placed in a waveguide directionperpendicular to the surfaces of the semiconductor substrate to opposeeach other, wherein the active layer is constituted by a quantum welllayer having a tensilely strain, and the second electrode is separatedinto portions not less than two portions.

With this arrangement, the oscillation mode of the apparatus is changedby selecting the numbers of the current injection electrodes, therebyproducing oscillation either in the TE mode or in the TM mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the arrangement of a semiconductorlaser apparatus according to the first embodiment of the presentinvention;

FIG. 2 shows a perspective view of the second embodiment of the presentinvention;

FIGS. 3A, 3B, and 3C show the third embodiment of the present invention,in which FIG. 3A is a sectional view taken along a line 3A-3A' in FIG.3C, FIG. 3B is a sectional view taken along a line 3B-3B' in FIG. 3C,and FIG. 3C is a plan view;

FIG. 4 is a plan view for explaining the structure of a semiconductorlaser apparatus according to the fourth embodiment of the presentinvention;

FIG. 5 is a system diagram showing an embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical information recording/reproducing apparatus;

FIG. 6 is a graph showing optical output-current characteristics toexplain an operation of the embodiment in FIG. 5;

FIGS. 7A to 7D are timing charts for explaining the operation of theembodiment in FIG. 5;

FIG. 8 is a view for explaining polarizing and reading operations of thesemiconductor laser apparatus in order to explain the operation of theembodiment in FIG. 5;

FIG. 9 is a view for explaining an operation of a photodiode in FIG. 5;

FIG. 10 is a system diagram showing a detailed arrangement of alight-receiving circuit in FIG. 5;

FIG. 11 is a system diagram showing another embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical information recording/reproducing apparatus;

FIG. 12 is a system diagram showing an embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical sensor;

FIG. 13 is a view for explaining an operation of the embodiment in FIG.12;

FIG. 14 is a block diagram showing a detailed arrangement of a signalprocessing circuit used for the optical sensor in FIG. 12;

FIG. 15 is a system diagram showing another embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical sensor;

FIG. 16 is a system diagram showing an embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical disk head;

FIG. 17 is a view for explaining an operation of the embodiment in FIG.16;

FIG. 18 is a system diagram showing an embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical encoder;

FIG. 19 is a view showing a detailed arrangement of a signal processingcircuit applied to the optical encoder in FIG. 18;

FIGS. 20A to 20D are timing charts for explaining an operation of thecircuit in FIG. 19;

FIG. 21 is a system diagram showing another embodiment in which thesemiconductor laser apparatus of the present invention is applied to anoptical encoder;

FIG. 22 is a system diagram showing an embodiment in which thesemiconductor laser apparatus of the present invention is applied to adisplay unit;

FIG. 23 is a view for explaining the relationship between a screen for ascanning beam, polarizing spectacles, and parallax in order to explainan operation of the embodiment in FIG. 22;

FIG. 24 is a block diagram showing a detailed arrangement of a drivingcontrol circuit in FIG. 22;

FIGS. 25A-25D are timing charts for explaining the operation of thecircuit in FIG. 24;

FIG. 26 is a view showing the relationship between a driving operationand the radiation position of a light beam in order to explain theoperation of the circuit in FIG. 24;

FIG. 27 is a system diagram showing another embodiment in which thesemiconductor laser apparatus of the present invention is applied to adisplay unit;

FIG. 28 is a view for explaining shift correction in FIG. 27; and

FIGS. 29A and 29B are views for explaining a conventional semiconductorlaser apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a semiconductor laser apparatus according to the firstembodiment of the present invention. The same reference numerals in FIG.1 denote the same parts or parts having the same functions as in FIGS.29A and 29B.

Referring to FIG. 1, a lower AlGaAs cladding layer 4, a GaAsP/AlGaAsstrain quantum well active layer 2 located on the cladding layer 4, andan upper AlGaAs cladding layer 3 located on the active layer 2 aresequentially formed on a GaAs semiconductor substrate 1. SiO₂ insulatinglayers 5a and 5b for current constriction are formed on the uppercladding layer 3. Upper Au electrodes 61 and 62 and a lower Au electrode7 are formed to sandwich the GaAs semiconductor substrate 1, the AlGaAscladding layer 4, the GaAsP/AlGaAs strain quantum well active layer 2,the AlGaAs cladding layer 3, and the SiO₂ insulating layers 5a and 5b.In this case, a central portion 3a of the upper surface of the AlGaAscladding layer 3 protrudes in one direction to form a refractive indexwaveguide, and the SiO₂ insulating layers 5a and 5b are spaced apartfrom each other and extend along this protruding portion 3a. The upperelectrodes 61 and 62 are spaced apart from each other and extend in adirection (perpendicular to the portion 3a, in this case) crossing theportion 3a of the cladding layer 3.

Note that the portion 3a of the upper AlGaAs cladding layer 3constitutes an optical waveguide stripe 10 for confining lightpropagating in a direction parallel to an optical waveguide in theactive layer 2 located under the portion 3a.

With this arrangement, the opposing side surfaces arranged in adirection perpendicular to the portion 3a serve as resonator mirrors 8and 9, respectively. In addition, the resonator mirrors 8 and 9constitute a Fabry-Perot resonator together with the members formedperpendicularly on the GaAs semiconductor substrate 1 and locatedbetween the resonator mirrors 8 and 9. The portion 3a of the upperAlGaAs cladding layer 3 is formed into the optical waveguide stripe 10to realize confinement of light propagating in a direction parallel tothe optical waveguide.

Light emitted upon injection of a current through the upper electrodes61 and 62 is guided to the optical waveguide stripe 10 to reciprocatebetween the resonator mirrors 8 and 9, thus causing laser oscillation.

In this case, total gains G_(TE) and G_(TM) respectively obtained, inthe TE and TM modes, from a given injected current within a resonatorlength L are represented by the following equations:

    G.sub.TE =g.sub.TE L -α.sub.TE L-ln(1/R.sub.TE)

    G.sub.TM =g.sub.TM L -α.sub.TM L-ln(1/R.sub.TM)

where g_(TE) is the gain obtained from the injected current in the TEmode, g_(TM) is the gain obtained from the injected current in the TMmode, α_(TE) is the waveguide loss per unit length in the TE mode,α_(TM) is the waveguide loss per unit length in the TM mode, R_(TE) isthe reflectance of each resonator mirror in the TE mode, and R_(TM) isthe reflectance of each resonator mirror in the TM mode. In a normaldescription, G_(TE) (G_(TM))<0 represents a non-oscillation state; andG_(TE) (G_(TM))≧0, an oscillation state. If oscillation can be producedin the two modes, oscillation is produced in one of the modes whichensures a higher gain, while oscillation in the other mode issuppressed.

With a given injected current, therefore, if the total gain G_(TE) ishigher than the total gain G_(EM), oscillation is mainly produced in theTE mode, and vice versa. This operation is expressed as follows:

    G=G.sub.TE -G.sub.TM =(g.sub.TE -g.sub.TM)L -(α.sub.TE -α.sub.TM)L-(ln(1/R.sub.TE)-ln(1/R.sub.TM))

If G>0, then oscillation is produced in the TE mode.

If G<0, then oscillation is produced in the TM mode.

In this case, if the length of the upper electrode 61 is represented byl, and the total length of the upper electrodes 61 and 62 is representedby L, (L>l),

    G=(g.sub.TE -g.sub.TM)l-(α.sub.TE -α.sub.TM)L-(ln(1/R.sub.TE)-ln(1/R.sub.TM))

In the case of a Fabry-Perot resonator,

    R.sub.TE >R.sub.TM

As disclosed in M. J. B. Boermans, S. H. Hagen, A. Valster, M. N. Finke,J. M. M. Van Der Heyden et al., "Investigation of TE and TM polarizedlaser emission in GalnP/AlGalnP lasers by growth-controlled strain",Electron. Lett., Vol. 26, p. 1438, 1990, if the tensilely strain amountof the quantum well layer of the active layer is controlled,recombination of electrons in a conduction band and light holes in avalence band becomes dominant. As a result, the following relation canbe established:

    g.sub.TE <g.sub.TM

In addition, since internal losses in the TE and TM modes are almost thesame,

    α.sub.TE =α.sub.TM

(Even if the losses are not the same, the following argument can besustained by causing the difference in loss to cancel out the differencein reflectance.) When a current is injected into only the electrode 61(length l)

    G=(g.sub.TE -g.sub.TM)l-(ln(1/R.sub.TE)-ln(1/R.sub.TM))>0

thus producing oscillation in the TE mode. When a current is injectedinto both the upper electrodes 61 and 62 (total length L),

    G=(g.sub.TE -g.sub.TM)L-(ln(1/R.sub.TE)-ln(1/R.sub.TM))<0

thus producing oscillation in the TM mode. Therefore, by selectivelyinjecting a current into one or both of the electrodes, the differencein gain between the two modes is mainly changed to allow selection ofthe TE or TM mode.

The following are examples of numerical values for such an operation:

Assume that R_(TE) =35%, R_(TM) =30%, and g_(TE) -g_(TM) =-10 cm⁻¹. Inthis case, if l<154 μm, then G>0, and oscillation is produced in the TEmode. If L>154 μm, then G<0, and oscillation is produced in the TM mode.

FIG. 2 shows the second embodiment of the present invention. The secondembodiment is different from the first embodiment in that a currentinjection region is divided into three portions or more. For thispurpose, upper electrodes 61, 62, and 63 are formed to be spaced apartfrom each other.

FIG. 3 shows the third embodiment of the present invention, in which astrain is applied to an active layer in advance such that the gains ofthe TE and TM modes become equal to each other. The third embodiment ischaracterized in that one (an upper electrode 62) of the divided currentinjection regions has no refractive index waveguide in a directionparallel to the substrate. For this reason, although a gain waveguide10b is formed while a current is injected, no waveguide is formed whileno current is injected. Therefore, light which propagates in this regionwhile a current is injected becomes almost parallel light. While nocurrent is injected, the light becomes divergent light and is reflectedby a resonator mirror 8. In consideration of the Fresnel reflectionformula, in this case, the reflectance of parallel light is higher thanthat of divergent light in the TE mode, whereas the reflectance ofdivergent light is higher than that of parallel light in the TM mode.

The above description will be summarized below. The reflection lossdifference between the two modes is changed according to thepresence/absence of a current injected into the upper electrode 62. Whena current is injected to form a gain waveguide, oscillation is producedin the TE mode. When no current is injected, oscillation is produced inthe TM mode.

FIG. 4 shows the fourth embodiment of the present invention, in which astrain is applied to an active layer in advance such that the gains ofthe TE and TM modes become equal to each other. The fourth embodiment ischaracterized in that a reflecting surface 11 is formed in a waveguide.The reflecting surface 11 formed in the waveguide is inclined withrespect to an optical axis perpendicular to resonator mirrors 8 and 9 ata Brewster angle θ of the TE mode. Therefore, the reflectance of the TEmode at the reflecting surface 11 becomes 0. In this case, when acurrent is injected into upper electrodes 61 and 62, the TE mode canreciprocate between the resonator mirrors 8 and 9 without undergoing areflection loss at the reflecting surface 11, whereas the TM modeundergoes a reflection loss of 30% or more at the reflecting surface 11.In this case, oscillation is produced in the TE mode. In contrast tothis, when a current is injected into the upper electrode 62 and anupper electrode 63, the TM mode can reciprocate between the resonatormirror 9 and a resonator mirror 12 while it is reflected by thereflecting surface 11 by 30% or more, whereas the TE mode undergoes areflection loss of 100% at the reflecting surface 11. In this case,oscillation is produced in the TM mode.

In the first to fourth embodiments, GaAsP/AlGaAs-based materials areused for the respective active layers. However, it is apparent thatother strain superlattice materials such as GaInp/AlGaInP- andGaInAs/GaInAsP-based materials can be used to obtain the same effects asthose described above.

As described above, the semiconductor laser apparatus of the presentinvention has the following unique effects:

(1) Polarization can be switched between the TE and TM modes by onlychanging the regions in which a current is injected without using arotating or moving mechanism. Therefore, the conversion speed is muchhigher than that in the conventional apparatus.

(2) A reduction in size and weight can be achieved to the same degree asthat of the conventional semiconductor laser apparatus.

(3) Since the apparatus of the present invention can be manufactured byadding simple steps, e.g., separation of electrodes, to themanufacturing process of the conventional semiconductor laser apparatus,an increase in the cost of an optical system can be minimized.

FIG. 5 shows the fifth embodiment of the present invention, in which theabove-described semiconductor laser apparatus is applied to an opticalinformation recording/reproducing apparatus. Referring to FIG. 5,reference numeral 101 denotes an magneto-optical disk; 102, an objectivelens; 103, a beam splitter; and 104, a TE/TM mode control semiconductorlaser according to the first embodiment of the present inventiondescribed with reference to FIG. 1. In addition, reference numeral 105denotes a cylindrical lens; 106, a polarizer/analyzer, a 107, aphotodiode; 108, a light-receiving circuit for obtaining a servo signalS1 and a reproduction signal from a signal detected by the photodiode107; 112, a clock circuit for supplying clock outputs CL1 and CL2 ofopposite phases shown in FIGS. 7A and 7B, respectively; 110 and 111,sample-and-hold circuits for receiving the outputs from thelight-receiving circuit 108 to sample/hold them on the basis of theclock outputs CL1 and CL2, respectively; 113, a differential amplifierfor obtaining an magneto-optical reproduction signal S4 from the outputdifference between the sample-and-hold circuits 110 and 111; 115, alaser driving circuit for supplying signals S6 and S7 (FIGS. 7A and 7B)for driving the semiconductor laser 104 on the basis of the clockoutputs CL1 and CL2; and 134, a bias magnet. Note that reference symbolst₁, t₂, . . . , t_(n), t_(n+1), . . . in FIG. 7 denote the timings ofthe respective clock pulses.

The photodiode 107 used in this case is divided into four elements 107a,107b, 107c, and 107d, for example, as shown in FIG. 9. The sum ofoutputs from these photodiode elements 107a to 107d is supplied to thelight-receiving circuit 108.

As shown in FIG. 10, for example, the light-receiving circuit 108 isconstituted by a plurality of operation elements such as AND gates 108ato 108e and operational amplifiers 108f and 108g. The light-receivingcircuit 108 receives outputs from the elements 107a to 107d of thephotodiode 107 and arithmetically processes them to output servo signalsS1, e.g., a focus error signal S1a and a track error signal S1b, and areproduction signal S2.

If the photodiode 107 and the light-receiving circuit 108 respectivelyshown in FIGS. 9 and 10 are used, a reproduction signal S4 output fromthe differential amplifier 113 becomes an output proportional to thetotal amount of light received by the photodiode 107.

The focus error signal S1a extracted by the light-receiving circuit 108is detected as follows. The shape of a focused beam spot changesdepending on the defocus amount of the objective lens 102 with respectto the magneto-optical disk 101. More specifically, as shown in FIG. 9,the shapes denoted by reference symbols BSa, BSb, and BSc appear whenthe defocus amount is positive, zero, and negative, respectively. Such adefocus amount is detected as the focus error signal S1a by a focusdetection optical system based on an astigmatism method using thecylindrical lens 105 on the basis of the difference between the sumsignal of the signals from the photodiode elements 107a and 107c andthat from the elements 107b and 107d.

The track error signal S1b is obtained from the difference between thesum signal of the signals from the elements 107b and 107c and that fromthe elements 107a and 107d.

In this case, the polarizing direction of the polarizer/analyzer 106 isset at 45° with respect to TE/TM mode polarized light.

In this arrangement, light which is emitted when a current is injectedinto upper electrodes 61 and 62 is guided to an optical waveguide stripe10 and reciprocates between resonator mirrors 8 and 9, thus producinglaser oscillation.

Assume that the total gains obtained, in the TE and TM modes, from agiven injected current within a resonator length L are respectivelyrepresented by G_(TE) and G_(TM) ; and the difference (G_(TE) -G_(TM)),G. In this case, when the difference G is positive, oscillation isproduced in the TE mode, whereas when the difference G is negative,oscillation is produced in the TM mode. If the gains obtained from theinjected current in the respective modes are represented by g_(TE) andg_(TM), respectively; the waveguide losses per unit length in therespective modes; α_(TE) and α_(TM), and the reflectances of therespective resonator mirrors in the respective modes, R_(TE) and R_(TM),the value of the difference G is given by

    G=(g.sub.TE -g.sub.TM)×X-(ln(1/R.sub.TE)-ln(1/R.sub.TM))

where x is the length of a current injection region, l is the lengthrequired for the TE mode oscillation, with which G>0, and L is thelength required for the TM mode oscillation, with which G<0.

For example, if R_(TE) =35%, R_(TM) =30%, and g_(TE) -g_(TM) =-10 cm⁻¹,then l<154 μm.

FIG. 6 shows examples of selective oscillation in the TE and TM modes,in which an injected current is plotted along the abscissa, and anoptical output is plotted along the ordinate, representing a resultobtained by measuring outputs in the TE and TM modes when currents areinjected with the lengths L and l, respectively.

Accordingly, light having different polarization states in the TE and TMmodes can be extracted while an optical output P₀ is kept constant, bycontrolling the current injection regions L and l and magnitudes i₁ andi₂ of the injected currents.

When oscillation is to be produced in the TM mode, a current is injectedinto the upper electrodes 61 and 62. According to the characteristicsshown in FIG. 6, the output P₀ of the TM mode can be obtained with themagnitude i₁ of the current.

When oscillation is to be produced in the TE mode, a current is injectedinto only the upper electrode 61. According to the characteristics shownin FIG. 6, the output P₀ of the TE mode can be obtained with themagnitude i₂ of the current.

When oscillation is alternately produced in the TM and TE modes, acurrent S6 supplied to the electrode 62 and a current S7 supplied to theelectrode 61 are controlled. More specifically, for TM mode oscillation,a current of the magnitude i₁ as the sum of both the currents S6 and S7is supplied to the electrodes 61 and 62. For TE mode oscillation, onlythe current S7 of the magnitude i₂ is supplied to the electrode 61. Forexample, at a timing t_(n) in FIGS. 7A to 7D, a current is injected intoonly the electrode 61, and hence the semiconductor laser 104 oscillatesin the TE mode.

This operation will be described below with reference to therelationship between each recording mark on the disk 101 and a beam spotshown in FIG. 8. Reference numeral 130 denotes a track on themagneto-optical disk 101; 131, magnetic recording marks on the track130; 132, a beam spot; and 133, the polarizing direction of the beamspot 132.

The interval between the timings t_(n), . . . , t_(n+3) in FIG. 8 issufficiently shorter than the moving time of the recording marks 131upon rotation of the disk 101 so that the relative positions of the beamspot 132 and the magnetic recording mark 131 only slightly change duringthe repeating interval of the polarizing direction 133 in the TE and TMmodes.

Assume that a 1-μm long recording mark on the disk 101 which is rotatingat a peripheral speed of 2 m/s is read with the repeating frequency ofthe TE and TM modes being set to be 200 MHz. In this case, since thescanning time for 1 μm is 500 ns, and the mode time interval is 5 ns,signal reproduction in the TE and TM modes for one mark can be performedby 100 repetitions.

As described above, reproduction signals S2 in the TE and TM modes canbe sampled by the sample-and-hold circuits 110 and 111 at a repeatinginterval sufficiently shorter than the scanning time of the beam spot132 with respect to the magnetic recording mark 131, and a differentialsignal, i.e., an optomagnetic reproduction signal S4, can be obtained bythe differential amplifier 113.

FIG. 11 shows another embodiment of the present invention, in which abirefringent prism is used in place of the polarizer/analyzer 106. Thesame reference numerals in FIG. 11 denote the same parts as in FIG. 5.Referring to FIG. 11, reference numeral 139 denotes a birefringent prismarranged after a cylindrical lens 105; 136a and 136b, photodiodesarranged after the birefringent prism 139 and designed to receive lightbeams LB1 and LB2; and 136, a differential amplifier for receivingoutputs from the photodiodes 136a and 136b.

The direction of the crystallographic axis of the birefringent prism 139is set such that when light beams of the TE and TM modes are incident,the amounts of the light beams LB1 and LB2 divided by the birefringentprism 139 becomes almost the same.

Light reception outputs ia and ib from the photodiodes 136a and 136b inthe TE and TM modes with respect to a Kerr rotation θ are analyzed by aJones matrix in the same manner as described above. The following arethe analysis results:

    |ia(TE)|.sup.2 =R/4·(1-SIN2θ)

    |ib(TE)|.sup.2 =R/4·(1+SIN2θ)

    |ia(TM)|.sup.2 =R/4·(1+SIN2θ)

    |ib(TM)|.sup.2 =R/4·(1-SIN2θ)

If, therefore, outputs S6 from the differential amplifier 136 in the TEand TM modes are respectively represented by i'_(TE) and i'_(TM), then

    i'.sub.TE =(R/2)SIN2θ

    i'.sub.TM =(R/2)SIN2θ

The outputs S6 from the differential amplifier 136 are supplied tosample-and-hold circuits 110 and 111 to be sampled/held. If adifferential output S4=(i'_(TE) -i'_(TM)) based on the differencebetween reproduction signals in the TE and TM modes, obtained by furthersupplying the outputs S6 to a differential amplifier 113, is representedby i"_(M0), the following equation can be established:

    i".sub.M0 =RSIN2θ

As is apparent from the above analysis, in this embodiment, detection ofthe Kerr rotation θ can also be performed by using magneto-opticalrecording marks.

Since the embodiment shown in FIG. 11 uses the birefringent prism 139 inplace of the polarizer/analyzer, the amount of light used for lightreception can be set to be large, and hence the embodiment is effectivewhen a high S/N ratio is required against circuit noise or the like, ascompared with the fifth embodiment.

In this case, the embodiment shown in FIG. 11 uses a triangular prismconsisting of a birefringent material as the birefringent prism. It is,however, apparent that the same effects can be obtained even with apolarizing prism formed by bonding Wollaston prisms to each other.

Referring to FIG. 5, assume that in a case wherein information isrecorded while a magnetic field is generated by the bias magnet 134, andthe temperature of the optomagnetic medium is raised to the Curietemperature or more to invert the magnet domains of the medium. It isapparent, even in this case, that a writing operation with respect tothe magneto-optical disk can be performed regardless of whether thelaser output is increased in the TE or TM mode.

FIGS. 12 and 13 show an embodiment in which the present invention isapplied to an optical sensor.

Referring to FIGS. 12 and 13, reference numeral 201 denotes asemiconductor laser apparatus capable of oscillation control in the TEand TM modes according to the present invention, which apparatus isshown in detail in FIGS. 1 to 4; 201a and 201b, electrodes of thesemiconductor laser apparatus 201; 202, a lens for receiving light fromthe semiconductor laser apparatus 201; 203, a beam splitter arrangedafter the lens 202; 204, a birefringent prism arranged between the beamsplitter 203 and a target object to be measured; 206, a target objectfor receiving light beams LB5a and LB5b obtained by the birefringentprism 204; 206a, a track on the target object 206; and 207, aphotodetector.

In this arrangement, the modes of polarized light can be selectivelycontrolled by controlling the amount of a current injected into theelectrodes 201a and 201b. The structure and oscillation principle of thelaser apparatus will be apparent from the detailed description of theprevious embodiments.

A light beam generated by the semiconductor laser apparatus 201 and thelens 202 is incident on the birefringent prism 204 to be refracted. If abirefringent material such as quartz, calcite, or titanium oxide is usedfor the prism 204, since the refractive index of the light beam differsdepending on its polarizing direction, the angle of refraction of thelight beam differs. In this case, in the TE mode, the vibratingdirection of an electric field, i.e., the polarizing direction, isparallel to the drawing surface of FIG. 12. In the TM mode, thepolarizing direction is perpendicular to the drawing surface of FIG. 12.If the crystal orientation of a prism material is determined in amanufacturing process such that the refractive index of the prism 204 ishigher in the TE mode than in the TM mode, light beams LB5a and LB5b canbe extracted in the TM and TE modes, respectively.

FIG. 13 shows an enlarged state of the light beams LB5a and LB5b and thetrack 206a. By only performing current injection control with respect tothe electrodes of the laser apparatus, polarization control in the TEand TM modes can be performed. As a result, light beams can be scannedover the track 206a so as to sandwich the track 206a. When lightreflected by the target object 206 reaches the beam splitter 203 throughthe birefringent prism 204, the optical path of the light is split bythe beam splitter 203, and the light is converted into an electricalsignal by the photodetector 207. The photodetector 207 detects changesin the refractive index of the light beams LB5a and LB5b of the TE andTM modes, reflected by the track 206a. If the target object 206 or theoverall optical sensor is moved by a positioning mechanism (not shown)such that these refractive index changes become equal to each other, therelative positions of the track and the optical sensor can be keptconstant. In this embodiment, since a polarizing mirror mechanism suchas a galvanomirror is not required, a compact, simple arrangement can berealized. In addition, polarization control in the laser apparatus canbe performed by only controlling current injection. Therefore, scanningof light beams can be performed at very high speed as compared with acase wherein an optical path is deflected by a mechanism.

FIG. 14 shows an embodiment of the present invention, specifically asignal processing circuit in the embodiment shown in FIG. 12. Referringto FIG. 14, reference numeral 221 denotes a clock signal generator; 222,a TE/TM mode laser oscillation control signal generator; 223 and 224,current driving circuits for the semiconductor laser apparatus; 225, ananalog switch; 226, an inverting amplifier; 227, a noninvertingamplifier; 228 and 229, sample-and-hold circuits; and 230, adifferential amplifier. In the embodiment shown in FIG. 14, light beamsLB12a and LB12b of the TE and TM modes are reflected by a target object10 and are separated by different photodetectors 211a and 211b so as tobe converted into electrical signals. This embodiment, however, requiresa lens 213, and the positions of the photodetectors and focusedreflected light beams must be adjusted. For this reason, the embodimentis disadvantageous in terms of a reduction in size and cost. The signalprocessing circuit shown in FIG. 15 is a circuit having a simple opticalarrangement such as the one shown in FIG. 12 and designed to separatelight beams of the TE and TM modes reflected by a target object andconverting them into electrical signals by using one photodetector in atime sharing manner. The timing of switching between the TE and TM modesis controlled by a clock pulse from the clock signal generator 221 insynchronism with the laser oscillation control signal generator 222, thecurrent driving circuits 223 and 224 for the semiconductor laserapparatus, the analog switch 225, and the sample-and-hold circuits 228and 229. The laser oscillation control signal generator 222 injects arequired current into electrodes 201a and 201b of the semiconductorlaser apparatus through the current driving circuits 223 and 224 toalternately switch the oscillation mode of the semiconductor laserapparatus (not shown) between the TE and TM modes. At the same time, anelectrical signal representing a reflectance change with respect to thetarget object, supplied from the photodetector 207 (not shown), isselectively distributed to either the inverting amplifier 226 or thenoninverting amplifier 227 by the analog switch 225 in synchronism witha clock. While intermittent signals are integrated by thesample-and-hold circuits 228 and 229, a differential signal 231 based onthe difference between outputs from the sample-and-hold circuits 228 and229 is obtained by the differential amplifier 230. The differentialsignal 231 obtained in this manner is a signal equivalent to adifferential signal based on the difference between electrical signalsfrom photodetectors 211a and 211b in FIG. 14. By using the electricalcircuit shown in FIG. 15, a differential signal based on detectionsignal obtained by detecting light beams of the TE and TM modes can bedetected by using one photodetector.

FIG. 15 shows still another embodiment in which the semiconductor laserapparatus of the present invention is applied to an optical sensor. Thesame reference numerals in FIG. 15 denote the same parts as in FIG. 12.

Referring to FIG. 14, reference numerals 209 and 213 denote lenses; 203,a beam splitter; 208, a Wollaston prism formed by bonding birefringentprisms to each other; and 211a and 211b, photodetectors. Referencesymbols LB12a and LB12b denote light beams.

Referring to FIG. 14, a light beam is generated by a semiconductor laserapparatus 201 which is formed as one unit and capable of performingpolarization control in the TE and TM modes according to the presentinvention shown in FIGS. 1 to 4, and a lens 202. The light beam is thenincident on the Wollaston prism 208 to be refracted. In this case, theWollaston prism 208 can extract the light LB12a in the TM mode, and thelight beam LB12b in the TE mode. The respective light beams are focusedon a target object 206 through the lens 209. Since the principle ofmeasurement of a track position of the object is the same as that in theabove embodiments, a description thereof will be omitted. Note, however,that since the beam splitter 203 for splitting the optical path of eachreflected light beam is arranged at the rear side of each optical pathof the Wollaston prism 208, the optical paths of the reflected lightbeams LB12a and LB12b, extending to the photodetectors 211a and 211b,are separated from each other. Therefore, the light beams LB12a andLB12b can be easily separated from each other spatially by the lens 213.

FIG. 16 shows an embodiment in which the present invention is applied toan optical head. FIG. 17 shows an enlarged state of an optical disk andlight beams. The same reference numerals in FIGS. 16 and 17 denote thesame parts as in FIG. 14.

Referring to FIGS. 16 and 17, reference numeral 240 denotes an actuatorfor positioning a lens 209; 241, an optical disk; 242, a beam splitter;243, a photodetector; 244, a track on the optical disk 241; 247, a guidegroove in the optical disk 241; 245, a data mark recorded on the opticaldisk 241; 246a and 246b, beam spots of the TE and TM modes; and 248, aservo signal detecting optical system. When the polarization mode of thesemiconductor laser apparatus is switched between the TE and TM modes,light beam is polarized by a Wollaston prism 208 according to thepolarization mode so that the beam spots 246a and 246b radiate the datamarks 245 while alternately moving over the adjacent tracks 244 on theoptical disk 241. The light beams reflected by the optical disk 241 aresplit by the beam splitters 203 and 208 and are converted intoelectrical signals by the photodetector 243. In this case, the opticaldisk 241 is rotated, and its linear speed is 5 m/s to 15 m/s if it has adiameter of 130 mm. Since switching of current injection to the laserapparatus to switch between the TE and TM modes is performed at a speedof 1 ns or less, parallel signals can be read almost at the same time.As described above, the beam spots 246a and 246b are alternatelyradiated on two tracks while the polarization mode of the semiconductorlaser apparatus 201 is switched between the TE and TM modes, therebyrealizing a parallel data reading operation.

FIG. 18 shows an embodiment in which the semiconductor laser apparatusaccording to the present invention is applied to an optical encoder.

Referring to FIG. 18, reference numeral 201 denotes a semiconductorlaser apparatus constituted by the single element shown in FIG. 1 andcapable of performing oscillation control in the TE and TM modes; 202, alens; and 203, a beam splitter. These components have the samearrangements as those in FIG. 12. Reference numeral 254 denotes abirefringent plate arranged after the beam splitter 203; 259, adiffraction grating scale; 261, a photodetector; and 255 and 256,mirrors respectively arranged between the birefringent plate 254 and thediffraction grating scale 259 and between the beam splitter 203 and thediffraction grating scale 259. Reference symbols LB17 and LB18 denotelight beams; and RLB1, a diffracted light beam.

A light beam generated by the semiconductor laser 201 and the lens 202is divided into two light beams by the beam splitter 203. One light beamLB17 is transmitted through the birefringent plate 254 and is reflectedby the mirror 255, and the other light beam LB18 is directly reflectedby the mirror 256 so that the two light beams LB17 and LB18 cross eachother on the diffraction grating scale 259 as an object to be measured.The diffracted light beam RLB1 deriving from the two light beams LB17and LB18 is detected as a coherent light intensity by the photodetector261.

In this arrangement, as the diffraction grating scale 259 linearlymoves, the light intensity signal obtained by the photodetector 261 ismodulated in the form of a sine wave. This light intensity signal ismodulated by an amount corresponding to two periods every time the scale259 is moved by one pitch. In this case, the birefringent plate 254 is aplane-parallel plate consisting of a birefringent material such asquartz, calcite, or titanium oxide. Since the reflectance differsdepending on the polarizing direction of a light beam, the optical pathlength between the beam splitter 203 and the mirror 255 can beelectrically changed by switching the polarization mode of thesemiconductor laser 201 between the TE and TM modes. More specifically,if the wavelength of a laser beam is represented by λ; the refractiveindex difference based on the polarization of the birefringent plate254, δn; and the thickness of the birefringent plate 254, T, then anoptical path length difference δφ is given by T/(λ·δn). Assume that theconstant of the birefringent plate 254 is set to establish δφ=1/4.. Inthis case, when the polarization mode of the semiconductor laser 201 isswitched between the TE and TM modes, the coherent light intensitysignal based on the diffracted light beam RLB1 in the TE mode and thatbased on the diffracted beam RLB1 in the TM mode shift in phase fromeach other by a 1/4 period. Therefore, a detection output indicating ascale position can be obtained by the photodetector 261, while thedetection output is modulated with the phase difference δφ set on thebasis of the optical path length difference at the birefringent plate254, by switching the oscillation mode of the semiconductor laser 201between the TE and TM modes at a period sufficiently shorter than theperiod at which an optical output from the photodetector 261 ismodulated by the movement of the diffraction grating scale 259. Thisoperation will be described below with reference to FIGS. 19 to 20D.

FIG. 19 shows a detailed arrangement of a system for processing a signaldetected by the photodetector 261. Referring to FIG. 19, referencesymbol S40 denotes an output from the photodetector 261; S41, a TE/TMmode control signal; S42, a TE mode detection signal; and S43, a TM modedetection signal. Reference numeral 251 denotes an amplifier foramplifying the signal S40 output from the photodetector 261; 252, aninverter for inverting the supplied TE/TM mode control signal S41; and253 and 254, sample-and-hold circuits for sampling/holding the outputfrom the amplifier 251 on the basis of the output from the inverter 252and the TE/TM mode control signal. Note that reference numeral 263denotes a TE/TM mode control signal generator for generating the TE/TMmode control signal S41 upon reception of a clock signal from a clocksignal generator 262.

An operation of the system shown in FIG. 19 will be described withreference to the timing charts in FIGS. 20A to 20D. When thepolarization mode of the semiconductor laser 201 is switched between theTE and TM modes, the detection signal S40 shown in FIG. 20A isintensity-modulated in the form of a sine wave in accordance with ascale moving amount x while it is modulated with the optical path lengthdifference δφ based on the polarization. In this case, δφ=1/4. is set,and an output from the amplifier 251, obtained by amplifying thedetection signal S40, is input to the two sample-and-hold circuits 253and 254 in accordance with the TE/TM control signal S41 shown in FIG.20B. The sampling/holding synehronization polarities of the twosample-and-hold circuits 253 and 254 are switched to output signals. Asa result, the TE mode detection output S42 shown in FIG. 20C and the TMmode detection output S43 shown in FIG. 20D can be separately output.These signals are 90° out of phase. By comparing the magnitudes of thetwo signals with each other, not only the distance the scale moves butalso its moving direction can be discriminated.

FIG. 21 shows another embodiment in which the present invention isapplied to an optical encoder using an optical waveguide, specificallyan optical system for performing interference detection while changingthe optical path length by polarization control. Referring to FIG. 21,reference numeral 321 denotes a semiconductor laser apparatus capable ofperforming oscillation control in the TE and TM modes according to thepresent invention; 322 and 323, waveguides; 324, a birefringentwaveguide; 325 and 326, lenses; 329, a diffraction grating scale; 331, alens; and 332, a photodetector. Reference symbols LB21 and LB22 denotelight beams; and RLB2, a diffracted light beam.

In the embodiment shown in FIG. 21, the bent waveguides 322 and 323,each having a refractive index optical guide layer consisting of, e.g.,quartz, PMMA, or polyimide, are formed at the two ends of the TE/TMcontrol semiconductor laser 321, and the waveguide 324 havingbirefringence is inserted in part of the waveguide 323. In this case,birefringence can be provided by applying a strain to a material havinga photoelastic effect, e.g., polyimide or polycarbonate, or by using anoptical anisotropic material, e.g., quartz or titanium oxide. The lenses325 and 326, each formed by mixing/stacking silicon oxide or siliconnitride to have a refractive index distribution in the verticaldirection and an aspherical shape in the horizontal direction, arerespectively arranged at two ends of the waveguides 322 and 323 so thatthe light beams LB21 and LB22 emitted from the waveguides 322 and 323are collimated and radiated on the diffraction grating scale 329 whilethe two light beams cross each other. The diffracted light beam RLB2from the diffraction grating scale 329 is focused on the photodetector332 through the lens 331, formed by the same method as that for thelenses 325 and 326, and the coherence light intensity of the diffractedlight beam RLB2 is detected. As in the description of the operation ofembodiment in FIG. 18, the refractive index of the birefringentwaveguide 324 differs depending on polarization of the TE/TM mode foroscillation of the semiconductor laser 321. However, by setting theoptical path length difference to be 1/4 the wavelength, the phasedifference between detection signals obtained by the photodetector 332during movement of the scale can be modulated by 90°. In signaldetection, similar to the description of the embodiments in FIGS. 19 to20D, while the oscillation mode of the semiconductor laser 321 isswitched between the TE and TM modes at high speed, a detection outputfrom the photodetector 332 is sampled/held by two sample-and-holdcircuits (not shown) in synchronism with switching between the TE and TMmodes, thereby separately extracting a detection output of the TE modeand a detection output of the TM mode. By using the detection signalswhich are 90° out of phase, obtained in this manner when the scale ismoved, the moving amount and direction of the scale can be measured.

FIGS. 22 and 23 show an embodiment in which the semiconductor laserapparatus according to the present invention is applied to a displayapparatus. FIGS. 25A to 25D show waveforms of currents to explain anoperation of the display apparatus.

Referring to FIGS. 22 and 23, reference numeral 201 denotes asemiconductor laser apparatus which is formed as a unit and capable ofperforming TE/TM mode control; and 202, a lens. These components areidentical to those shown in FIGS. 1 to 12, as in the above description.Reference numerals 373 and 374 denote galvanomirrors; 375, a lens; and376, a screen. Reference symbol LB27 denotes a light beam. Referencenumerals 378 and 379 denote patterns irradiated with light; and 380,polarizing spectacles. Referring to FIGS. 25A to 25D, reference symbolsS51 and S52 denote galvanomirror driving currents; and S53 and S54,laser driving currents.

The light beam LB27 generated by the semiconductor laser apparatus 201and the lens 202 is polarized by the galvanomirrors 373 and 374 indirections θx and θy and is focused by the lens 375. The light beam LB27is then scanned on the screen 376 in x and y directions. Upon modulationof the light intensity and polarization of the semiconductor laserapparatus 201 in synchronism with the deflecting/scanning operation ofthis light beam, an image or the like is displayed on the screen 376. Ina stereoscopic display operation, as shown in FIG. 23, the patterns 378and 379 scanned/irradiated with light beams having differentpolarization states are observed by an observer (not shown) wearing thepolarizing spectacles 380. The observer then can recognize astereoscopic effect because of the parallax. On the screen 376, the twopatterns corresponding to the parallax, the patterns of the character"A" in this case, are displayed by light beams having differentpolarization states so as to be shifted from each other by δL. In orderto realize this, as shown in FIGS. 25A to 25D, the driving current S51for the galvanomirror 374, supplied in the form of a sawtooth wave,scans the light beam LB27 in the x direction, and the driving currentS52 for the galvanomirror 373, supplied in the form of a stepped wave,scans the light beam LB27 in the y direction, while the driving currentS54 for causing laser emission in the TM mode is supplied to thesemiconductor laser apparatus 201 with a delay δT with respect to thedriving current S53 for causing laser emission in the TE mode. In thiscase, if the width by which the light beam LB27 is scanned on the screen376 in the x direction is represented by L, and the sawtooth wave periodof the driving current S51 for the galvanomirror 373 is represented byT, a desired parallax can be obtained by setting δT=δL×T÷L.

As described above, by performing emission control of the semiconductorlaser apparatus in the TE and TM modes in accordance with a parallaxwhile scanning a light beam two-dimensionally with the galvanomirrors, athree-dimensional display can be realized with a simple, compact opticalsystem.

FIG. 24 is a view for explaining polarization mode control of a lightbeam, shown in FIG. 22, and a deflection control circuit for thegalvanomirrors. FIG. 26 is a view for explaining a scanning operation ofa light beam.

Referring to FIGS. 24 and 26, reference numeral 431 denotes a computer;432, a clock generator; 433 and 434, frame memories; 435 and 436, pulsegenerators; 437, a delay circuit; 348, a TE mode laser driving circuit;439, a TM mode laser driving circuit; 440, a sync signal converter; 441,a horizontal scanning circuit; 442, a vertical scanning circuit; 443 and444, galvanomirror driving circuits; 451a, 451b, and 451c, TE mode beamspots; and 452a, 452b, and 452c, TM mode beam spots.

Emission control of the semiconductor laser apparatus in the TE and TMmodes in accordance with a parallax while scanning a light beamtwo-dimensionally with the galvanomirrors is performed by using thecontrol circuit shown in FIG. 24 in the following manner.Three-dimensional display image data based on a parallax and created bythe computer 431 are respectively stored in the two frame memories 433and 434 in synchronism with a sync signal from the clock generator 432,and are output to the pulse generators 435 and 436 for driving thesemiconductor laser apparatus 201, thereby causing the semiconductorlaser apparatus 201 to emit light in the form of a pulse while switchingbetween the polarization modes by using the laser driving circuits 438and 439. In this case, the sync signal from the clock generator 432 isinput to the horizontal scanning circuit 441 to cause a galvanomirror(not shown), through the galvanomirror driving circuit 443, to perform ascanning operation in the form of a sawtooth wave in a horizontaldirection (θx direction in FIG. 22). The sync signal is also input tothe vertical scanning circuit 442 to cause a galvanomirror (not shown),through the galvanomirror driving circuit 444, to perform a scanningoperation in the form of a stepped wave in a horizontal direction (θydirection in FIG. 22). These scanning operations of the galvanomirrorscorrespond to horizontal and vertical scanning of a TV signal, and hencewriting and reading operations with respect to the frame memories 433and 434 by horizontal and vertical scanning are completely synchronized.The delay circuit 437 is a circuit for slightly delaying laseroscillation in the TM mode relative to laser oscillation in the TE modewhen it is required to radiate light beams polarized in the TE and TMmodes at the same position on the screen. As shown in FIG. 26, radiationof light beams of the two polarization modes can be performed atsubstantially the same position by performing radiation of the beam spot451a of the TE mode and radiation of the beam spot 452a of the TM modewith a short delay time set therebetween by performing short-time pulseoscillation. In addition, light beams are not continuouslyemitted/radiated but are intermittently emitted/radiated in the scanningdirections of the light beams, as the beam spots 451a, 451b, and 451c inFIG. 26. If, however, the scanning speed is set such that the beam spotsare seen to be continuous owing to an after image effect, or a screenhaving an after image effect is used, no problems are posed.

FIG. 27 shows another embodiment in which the semiconductor laserapparatus according to the present invention is applied to a displayapparatus. This embodiment discloses the optical arrangement of adisplay apparatus having an optical element for correcting thedifference between the radiation position of the beam spot 451a of theTE mode and that of the beam spot 452a of the TM mode shown in FIG. 26.FIG. 28 is a view for explaining an operation of the optical element forcorrecting the difference. Reference numeral 460 denotes a birefringentprism 460. Reference symbol LB61 denotes a light beam incident on thebirefringent prism 460; and LB62 and LB63, light beams refracted by thebirefringent prism 460.

As described with reference to FIG. 26, even in a case wherein TE and TMmode polarized light beams need to be radiated at the same position onthe screen 376, since the two modes cannot be oscillated at the sametime, laser oscillation in the TM mode is produced slightly after laseroscillation in the TE mode. As a result, in the display apparatus shownin FIG. 22, the beam spot 451a of the TE mode and the beam spot 452a ofthe TM mode differ in position from each other. For this reason, asshown in FIG. 27, the birefringent prism 460 is arranged in the opticalpath between lenses 202 and 375 to return the beam spot 452a of the TMmode to the position of the beam spot 451a of the TE mode by means ofrefraction through the prism 460 upon polarization of the TE and TMmodes, thereby correcting the difference in position. That is, in FIG.28, the difference can be corrected by setting a difference δφ in angleof refraction between the light beam LB63 refracted in the TM mode andthe light beam LB62 refracted in the TE mode to satisfy δX=f×tan(δφ)where δX is the difference in position between the light beams 451a and452a in FIG. 26, and f is the focal length of the lens 375 in FIG. 27.

With this arrangement, by performing emission control of thesemiconductor laser apparatus in the TE and TM modes in accordance witha parallax while scanning a light beam two-dimensionally with thegalvanomirrors, three-dimensional display can be realized by using asimple, compact optical system instead of an optical arrangement of twodisplay elements or light beams positioned with high precision as in aconventional display apparatus.

What is claimed is:
 1. A semiconductor laser apparatus comprising:asemiconductor substrate having a first electrode on one surface; a firstcladding layer formed on the other surface of said semiconductorsubstrate; an active layer placed on said cladding layer; a secondcladding layer placed on said active layer; a second electrode placed onsaid second cladding layer; and a pair of resonator mirrors placed in awave guide direction perpendicular to the surfaces of said semiconductorsubstrate to oppose each other and constituting opposing side surfacesof said wave guide, wherein said active layer is constituted by aquantum well layer having a tensilely strain, and said second electrodeis separated into portions not less than two portions in a propagatingdirection of light in said wave guide.
 2. An apparatus according toclaim 1, wherein a strain is applied to said active layer such that again of a TM mode is not less than that of a TE mode.
 3. An apparatusaccording to claim 1, wherein said second cladding layer has aprotruding portion constituting a refractive index waveguide at aportion corresponding to one of said divided electrodes and extending ina direction to cross the surface of said semiconductor substrate.
 4. Anapparatus according to claim 3, wherein a portion, of said secondcladding layer, corresponding to the other electrode of said dividedelectrodes is made flat so as not to form a refractive index waveguide.5. An apparatus according to claim 1 further comprising:a slantedresonator mirror placed between the opposing side surfaces of said waveguide at a Brewster angle of a TE mode.